If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You must register
before you can post: click the register link above to proceed. To start viewing posts,
select the forum that you want to visit from the list below.

500.8(B)(3) Suitability of Equipment

I keep flipping between 500.8 and 501.105. My question about 500.8(B)(3) is that it says "Where specifically permitted in articles 501 through 503, general purpose equipment...shall be permitted in CID2 location if the equpment does not constitute a source of ignition."

What I would like this to say would be "General purpose equipment...shall be permitted in CID2 locations if the equipment does not constitute a source of ignition". It does not say this however, and says that the equipment has to be specifically permitted in 501 through 503.

So just reading 500.8(B)(3), then you are limited to just Transformers, Capacitors, Meters, Instruments, Relays, Motors... that are specifically described in article 501. If the electronics equipment is not a "Meter, Instrument, or Relay" for example, then the exception in 500.8(B)(3) would not be of any use.

So would it then be 500.8 (A)(3) alone that would allow someone to use an electronics device that is not an Instrument, Meter, or Relay in a CID2 area if the evaluation/evidence provided for the device show that it does not have any exposed surfaces that operate at temperatures in excess of the AIT of the specific gas or vapor, and the device is non arcing or sparking?

For example, a PLC. I know most are labelled for CID2, but if it were not, would I be able to consider it an "Instrument" and use the analysis from 501.105? If it is not considered an instrument, then what?

I keep flipping between 500.8 and 501.105. My question about 500.8(B)(3) is that it says "Where specifically permitted in articles 501 through 503, general purpose equipment...shall be permitted in CID2 location if the equpment does not constitute a source of ignition."

What I would like this to say would be "General purpose equipment...shall be permitted in CID2 locations if the equipment does not constitute a source of ignition". It does not say this however, and says that the equipment has to be specifically permitted in 501 through 503.

So just reading 500.8(B)(3), then you are limited to just Transformers, Capacitors, Meters, Instruments, Relays, Motors... that are specifically described in article 501. If the electronics equipment is not a "Meter, Instrument, or Relay" for example, then the exception in 500.8(B)(3) would not be of any use.

So would it then be 500.8 (A)(3) alone that would allow someone to use an electronics device that is not an Instrument, Meter, or Relay in a CID2 area if the evaluation/evidence provided for the device show that it does not have any exposed surfaces that operate at temperatures in excess of the AIT of the specific gas or vapor, and the device is non arcing or sparking?

For example, a PLC. I know most are labelled for CID2, but if it were not, would I be able to consider it an "Instrument" and use the analysis from 501.105? If it is not considered an instrument, then what?

Make a Public Input for the 2023 NEC; then you will know whether your insecurities are warranted or not. Meanwhile, memorize the last sentence of Section 90.1(A), which BTW, as long as Bill Fiske is a member of CMP14 and the TCC, is the answer you are likely to get.

Understood, I think about 90.1(A) often. I am not trying to use the NFPA 70 as a design guide, but as a means to make sure that equipment as a whole will meet the requirements of the AHJ.

To me, to use general wiring methods inside identified enclosures, then 500.8(A)(3) would be very relevent. The burden of proof would be on the manufacturer of the equipment to provide satisfactory evidence. If the wiring is not explicitly prohibited by the Articles 500-503, then the reasoning would be that it has been "identified" as suitable. That would apply to wiring, as well as to the rest of the equipment as a whole.

I think my wiring question should have been "Is it prohibited to use THHN or MTW inside of general purpose enclosure that has been identified for CID2". My evaluation for this would be that it is acceptable inside the enclosure because all of the components have been identified for Class I Div 2, and that using standard wiring methods inside the enclosure does not create a hazardous situation. And the clarification i need is that the "wiring methods" as outlined in article 501 do not apply inside enclosures.

And the same reasoning would apply to electronics components. The burdon of proof on the OEM would be to provide satisfactory evidence that the equipment is suitable, and that it is not specifically prohibited in article 500-503.

NOTE: I have chosen to use the 2014 NEC because it’s easier to understand for the purposes of this discussion. The 2017 added content that is basically unnecessary to the discussion but the analysis would be the same. Underlines are mine. (rbalex)

90.3 Code Arrangement. This Code is divided into the introduction
and nine chapters, as shown in Figure 90.3. Chapters
1, 2, 3, and 4 apply generally; Chapters 5, 6, and 7 applyto special occupancies, special equipment, or other specialconditions. These latter chapters supplement or modify thegeneral rules. Chapters 1 through 4 apply except as amendedby Chapters 5, 6, and 7 for the particular conditions.

Chapter 3 Wiring Methods and Materials

Art 310 Conductors for General Wiring

310.10 Uses Permitted. The conductors described in
310.104 shall be permitted for use in any of the wiring
methods covered in Chapter 3 and as specified in their
respective tables or as permitted elsewhere in this Code.

310.104 Conductor Constructions and Applications. Insulated
conductors shall comply with the applicable provisions
of Table 310.l04(A) through Table 310.104(E).Table 310.104(A) Conductor Applications and Insulations Rated 600V
(Table to be reviewed as an exercise for the student but both MTW and THHN are found in it).

…(4) Boxes and Fittings. Boxes and fittings shall not be required to be explosionproof except as required by 501.105…

As we can see Chapter 5 modifies, but does not replace Chapters 1, 2, 3, and 4.
Conductors and enclosure are part of wiring methods.
THHN and MTW can be used specifically, but not necessarily explicitly, in Chapter 3 enclosures.
THHN and MTW can be used specifically, but not necessarily explicitly, in Section 501.10 enclosures modified as necessary.

Just read all of the code references you mentioned above, and it gives me a lot to think about. I like the approach of "modify but does not replace", which also obviously mean if it does not mention, it does not modify. Thanks for taking the time for a thorough response!

It’s important to recognize that you will rarely fine the “whole” answer in one location in the NEC.

You should also be aware what Section 500.8(A) is actually about. I was one of its original authors back in 2002. In both the 1999 and 2002 cycles, the IAEI was practically demanding that all equipment used in classified locations be specificallylisted/labeled for the locations. Mainly because most inspectors were clueless (they admitted it). It was rejected in 1999 so they wanted everything identified in 2002. They assumed that meant listed or labeled. It doesn't, but the FPN/IN for identified in Art 100 strongly gives the impression that it does. There were too many products that were perfectly acceptable in Class I, II or III, especially in their respective Division 2 without specific listing or labeling ​for the location. For example, many GP motors in Class I, Division 2. In fact, most GP motors still aren't listed at all. Virtually all Interests except "Enforcement" and UL rejected the IAEI Proposal.

CMP14 attempted to create its own definition of identified applicable only to Articles 500-516. This was rejected by both CMP1 and the TCC. So we settled more-or-less on defining "Suitable". We based it on FedOSHA's definition of Acceptable in 29 CFR 1910.399. However, Section 500.8(A)(3) was made a bit more open ended. This was to allow new product technologies acceptable in future NEC's to be used as well as manufacturer or engineer evaluations. That is, if a future product was acceptable in a subsequent NEC, that was pretty good evidence that it should be acceptable for "engineering judgement" where many jurisdictions aren't "up-to-date" with the latest Code. ​

Since then, many products have indeed begun to secure listing/labeling. (Most GP motors still haven't.) BTW, RMC and several other listed products are notspecificallylisted for hazardous locations either. You can only use them because the Code says you can.

Last edited by rbalex; 06-14-18 at 06:04 PM.
Reason: Added the "not" in the last paragraph